Mi perro es tan fiel como mi mejor amigo.

My dog is as loyal as my best friend.

Breakdown of Mi perro es tan fiel como mi mejor amigo.

• el amigo: the friend
• el perro: the dog
• ser: to be
• mi: my
• mejor: best
• como: as
• tan: as
• fiel: loyal

Questions & Answers about Mi perro es tan fiel como mi mejor amigo.

What does tan fiel como mean, exactly? Is it like “as faithful as”?

Yes. Tan … como with an adjective means “as … as”.

• tan fiel como = as faithful/loyal as
• Structure: tan + adjective + como + comparison term

So:

• Mi perro es tan fiel como mi mejor amigo.
  = My dog is as faithful as my best friend.

It expresses equality in the quality described by the adjective (fiel).

Why is it tan fiel and not tanto fiel?

In Spanish:

• tan is used with adjectives and adverbs
  
  • tan fiel, tan alto, tan rápido
• tanto / tanta / tantos / tantas is used with nouns
  
  • tanto dinero (so much money)
  • tantos amigos (so many friends)

Because fiel is an adjective, you must say tan fiel, not tanto fiel.

Compare:

• Mi perro es tan fiel como mi mejor amigo.
  My dog is as faithful as my best friend.
• Tengo tantos amigos como tú.
  I have as many friends as you.

Why is it es and not está? Could I say Mi perro está tan fiel como…?

No, here you need es because fiel is seen as a characteristic / trait, not a temporary state.

• ser is used for:
  • essential characteristics: es fiel, es alto, es simpático
• estar is used for:
  • temporary states or conditions: está cansado, está enfermo

Loyalty is considered a more permanent trait, so you say:

• Mi perro es fiel. (He is loyal, as a characteristic.)

Mi perro está fiel would sound wrong or at least very strange in standard Spanish.

Does fiel change for masculine/feminine or singular/plural? Why not fiela?

Fiel is one of the adjectives that does not change for gender:

• masculine singular: un perro fiel
• feminine singular: una perra fiel

For the plural, it adds -es:

• masculine plural: unos perros fieles
• feminine plural: unas perras fieles

So in your sentence:

• Mi perro es tan fiel como mi mejor amigo.
  perro = masculine singular → fiel (not fielo or fiela)

Why is it tan fiel como and not fiel tan como or tan como fiel?

The structure tan + adjective + como is fixed in Spanish. You can’t move tan or como around.

✅ Correct:

• Mi perro es tan fiel como mi mejor amigo.

❌ Incorrect:

• Mi perro es fiel tan como…
• Mi perro es tan como fiel…

So always use: tan + adjective/adverb + como + noun/pronoun.

Why is it mi mejor amigo and not mi amigo mejor?

With mejor (better/best), the normal, natural position is before the noun:

• mi mejor amigo = my best friend
• mi mejor trabajo = my best job

You can sometimes see amigo mejor in special literary or poetic contexts, but in everyday Spanish from Spain, the standard is:

• mi mejor amigo, not mi amigo mejor.

So the sentence uses the usual, idiomatic order.

Why do we use como here and not que, like in más fiel que?

Spanish uses different words for different kinds of comparison:

• Equality (as … as):
  • tan fiel como = as faithful as
• Inequality (more/less … than):
  • más fiel que = more faithful than
  • menos fiel que = less faithful than

So:

• Mi perro es tan fiel como mi mejor amigo.
  My dog is as faithful as my best friend. (equality)

If you wanted to say your dog is more faithful, you’d say:

• Mi perro es más fiel que mi mejor amigo.

Why is it mi perro and not el perro or el perro mío?

You want to express possession, so you use the unstressed possessive adjective:

• mi perro = my dog
• tu perro = your dog
• su perro = his/her/their/your (formal) dog

You could say el perro mío, but:

• mi perro is more common and more neutral.
• el perro mío sounds more emphatic or stylistic, like “that dog of mine”.

So for a normal sentence, mi perro is exactly what you should use.

Why don’t we say como a mi mejor amigo with the personal a?

The personal a is used mainly with direct objects that are people (or personified animals):

• Veo a mi amigo. (I see my friend.)
• Quiero a mi perro. (I love my dog.)

In your sentence, mi mejor amigo is not a direct object; it is simply the second term in a comparison with como:

• tan fiel como mi mejor amigo

Because it’s not a direct object, you do not use the personal a here. So:

• ✅ tan fiel como mi mejor amigo
• ❌ tan fiel como a mi mejor amigo

Could I say the same idea in another way, like igual de fiel que?

Yes, a very common alternative in Spain is:

• Mi perro es igual de fiel que mi mejor amigo.

This also means “My dog is just as faithful as my best friend.”

Patterns:

• tan + adjective + como
  
  • tan fiel como
• igual de + adjective + que
  
  • igual de fiel que

Both are natural and correct; tan … como is slightly shorter and very frequent, but igual de … que is also very common.